Circuit controlling system

ABSTRACT

Disclosed is a method and device for controlling an electric circuit with the use of an electret with a rear electrode. The electric energy or signal transfer state of a field effect transistor is regulated by varying the electric field between the electret and an induction electrode, the field effect transistor being electrically connected to the combination of the electret and the induction electrode. The electric energy transfer state of the field effect transistor is regulated in response to the variation of the electric field, whereby the electric circuit to which the transistor is coupled is controlled.

United States Patent 1111 Uchikawa Apr. 1, 1975 1 1 CIRCUIT CONTROLLINGSYSTEM 2,708,746 5/1955 Shaw 331/65 X I 3.300.585 1/1967 Reedyk et a1.307/88 ET [751 Invent Uchlkawai JaPm 3.392.349 7/1968 Hartley 331/65[73] Assignee: Kureba Kagaku Kogyo Kabushiki 314361492 4/1969 i 179/111E Kaisha Tokyo japan 3.543.056 11/1970 Klem 328/5 x 3.571.666 3/1971McGuirk, .lr 340/258 C X [22] Filed: Sept. 27, 1973 3,588,549 6/1971Buch 307/309 3.646.372 2/1972 Snellman et al. 307/308 1 PP 40111963.748.727 7/1973 Swain 307/88 ET x Related US. Application Data [62]Division of Ser. No. 125,791, March 18. 1971. ""'7 James abandonAssistant ExammerL. N. Anagnos Attorney, Agent, or FirmSughrue,Rothwell, Mion. [30] Foreign Application Priority Data and Macpeak arJapan 45 22660 ABSTRACT 152] US. Cl 307/308, l78/DlG. 10, 179/111 E,Disclosed is a method and device for controlling an 307/88 ET, 307/251,328/5. 331/65, 340/258 electric circuit with the use of an electret witha rear 13 357/2 electrode. The electric energy or signal transfer state[51] I 1, C1, G031 13 2 HOl 7 02 04; 19 00 of a field effect transistoris regulated by varying the [58] Field of S arch 178/916, 179 110 1:electric field between the electret and an induction 179/111 307/33 ET251; 32 1 5; electrode, the field effect transistor being electrically331/; 340/258 R, 258 B. 258 C; 357/26 connected to the combination ofthe electret and the induction electrode. The electric energy transferstate 156] References Ci d of the field effect transistor is regulatedin response to UNITED STATES PATENTS the variation of the electricfield, whereby the electric l 804 364 5/193] Parker rig/DIG O circuit towhich the transistor is coupled is controlled. 2.663.802 12/1953Ohmart.........::::i::...::::... 307/88 ET 9 Claims, 8 Drawing FiguresNETS FIG.

FIG.

FIG 5 8 5 20 'i 62 A f? I93 9 s FIG. 6

SYN PH MOTOR DET OUTPUT I SIGNAL CIRCUIT CONTROLLING SYSTEM This is adivision of application Ser. No. 125,791, filed Mar. l8, i971, and nowabandoned.

FIELD OF THE INVENTION This invention relates to a system of controllingan electric circuit by the use of an electret. More particularly theinvention pertains to a method and device for controlling an electriccircuit by changing the electric signal or energy transfer condition ofa field effect transistor by varying the electric field between theelectret and an induction electrode coupled to the transistor.

SUMMARY OF THE INVENTION In accordance with the present invention, theconductive state of a field effect type active element, such as a fieldeffect transistor (FET) is changed in response to the operation ofdisplacing an electret, induction electrode, field shielding plate andthe like where the field effect transistor is electrically connected tothe induction electrode and electret. The present invention is based onthe phenomena that, in a combination of an electret and an inductionelectrode which is coupled to the electret by an electrostatic inductioneffect and the electric field caused by the electret, the electrostaticcapacitance between the electret and the induction electrode is variedby variation of the gap between the electret and the inductionelectrode, or by entrance and exit of the field shielding plate relativeto that gap. By appropriately selecting the operation characteristics ofthe FET and the electrical characteristics of input and output circuits,variation of the conductive state can be made two-positional, discretiveor continuous in response to the displacement of the electret inrelation to the induction electrode. Thus, on the basis of the foregoingprinciple, there is provided electric energy control devices such asswitches, variable resistors, and potentiometers, realized without theuse of electric contacts.

The relationship between the electret and the induction electrode issuch that, when the induction electrode consists of a conductive orsemiconductive body, grounded, or having large capacitance withoutspecifically being connected to earth, the ratio of strength of theelectric field between the inside and outside of the electret varies inresponse to approach of the body to the electret. This variation of thestrength can be sensed by a FET connected to, for example, a rearelectrode mounted on the rear surface of the electret. Thus, it may beconsidered to provide in accordance with the foregoing principle ofoperation a proximity switch which operates through, particularly, theelectric field of the electret.

Further, it is possible to transform the electric field caused by theinteraction a sector-shaped electret with an induction electrode of thesame shape into an oscillating field by vibrating or rotating theelectret; and to vary the oscillating electric field by positionaldisplacement of the sector-type induction electrode, by approach ofanother induction electrode, or by entrance and exit of an electricfield shielding plate relative to the field, and to thereby actuate theFET.

Generally, the input impedance of an FET has, when its gate is used asan input end, a significantly large value irrespective of a small andlarge signal input. Particularly, since a junction type FET (J-FET) doesnot have a threshold voltage as does an MOS-F ET, the output resistanceof the J-FET in the unsaturated region of the drain current is modulatedsubstantially linearly by an input voltage.

On the otherhand, the MOS-FET has a small leakage current at the gateterminal and a threshold voltage (for example, the enhancement typeMOS-FET), so that the characteristics of this type FET are beneficial inmaking sure of the OFF state in case the output characteristic has to betwo-positional or to provide a switch-like operation. The FET of theabove type can be driven by electrostatic induction action through theelectret. But, if the ON state of an input circuit is static, thelowering of the gate potential is large. Thus, the operation of the FETlags or becomes out of phase. This lowering of the gate potential isunavoidable to a certain degree. Thus, in the present invention it ispreferable to use a varying input signal.

However, the rate of potential lowering depends on the time constant ofthe input circuit, or, basically, on the gate leakage current of the FETas used and the polarization charge density and electrostaticcapacitance of the electret. In a feature of the present invention thereis provided an electret having a significantly large charge density andelectrostatic capacitance as the latter element whereby semi-staticoperation has been realized.

The electret having such characteristics as above may be made from highmolecular material such as polystyrene, polymetylmethacrylate,polytetratluoroethylene, polyfluorovinylidene, polyfluorovinyl,polycarbonate and polyethylenetelephthanlate, as well as various ceramicmaterials. Among the aforementioned materials, especially,polyfluorovinylidene there is realized remarkably high polarizationcharge density and dielectric constant. Thus, it allows the objects ofthe present invention to be realized and is suitable for stabilizationof operation and miniaturization of the applied devices.

There are two types of electrets; the polarization type in whichpermanent electric polarization or mutually separated positive andnegative independent charges are held in a balanced state, and theso-called monopole type in which in appearance a sole charge is held.Either one of the two types of the electret can be used.

Therefore, it is an object of the present invention to provide a systemof controlling an electric circuit by the use of an electret.

It is another object of the present invention to provide a method ofcontrolling an electric energy transfer state of a field effecttransistor by the use of an electret.

It is still another object of the present invention to provide a methodof controlling an electric circuit by the use of an electret in whichthe electric field of the electret is varied by movement of a body aswell as the electret whereby the energy transfer state of an associatedfield effect transistor is regulated.

It is a still further object of the present invention to provide devicesadapted to achieve the above-noted methods.

Therefore, in accordance with the present invention, there is provided asystem of controlling an electric circuit by the use of an electretwhich is characterized in that the electric field between the electretwith a rear electrode and an induction electrode is varied by movementof a body relative to the electric field or of the electret relative tothe induction electrode, whereby a field effect transistor electricallyconnected to the electret and the induction electrode is regulated withrespect to its electric signal or energy transfer condition. Further,there is provided a combination of the electret with a rear electrode,an induction electrode, and a field effect transistor electricallycoupled to the formers, which operates in such a manner that theelectric field appearing between the electret and the inductionelectrode is varied or modified in response to approach of a body ormovement of the electret relative to the induction electrode whereby theelectric energy or signal transfer state of the field effect transistoris accordingly changed with the result that any external electriccircuit connected to the transistor can be controlled. Thus, the presentinvention can be realized in the form of contactless switch, contactlessvariable resistor, contactless potentiometer and the like.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 and 2 are schematic views ofcontactless resistance regulators embodying the operation principle ofthe present invention;

FIG. 3 is an explanatory view of the operation of a contactless switchconstructed according to the principle of the present invention;

FIG. 4 is a structural view of the contactless switch shown in FIG, 3;

FIGS. 5 and 6 show embodiments of the proximity switch embodying theprinciple of the present invention; and

FIGS. 7A and 7B show parts of the proximity switch shown in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Now, several examples of theelectric system according to the present invention will be describedwith reference to the drawing, which utilize, as a control technique,variation of the electric field of the electret resulting from movementof any body, particularly, the related phenomena between displacement ofthe electret or an external body and corresponding variation ofelectrical conductivity of a field effect transistor connected to theelectret and induction electrode.

EXAMPLE 1 In FIGS. 1 and 2, the electric field caused by a plateelectret I with a rear electrode 2 plated thereto acts through a gap 4and causes electric charge to be induced on an induction electrode 3which is connected to a gate terminal G of an FET 5. Thus, a biasvoltage is produced between the gate G and source S of the FET, whereby,due to this voltage, the electric conductivity between the source S anddrain D is modified.

In this case, if a J-FET (for example, an N-channel depletion typeJ-FET) having no threshold voltage is used as the FET and if it isoperated in the unsaturated region of drain current, it is possible tochange the electric conductivity of the FET over a relatively wide range(5 X 10' u 5 X IO' u Thus, there is obtained a contactless variableresistor or potentiometer operable in response to displacement of theelectret or any body.

In case of FIG. I, if the electret l is displaced or moved towards oraway from the induction electrode 3 or in the directions of the opposingaxis therebetween, the electric resistance between the electrodes 5 andD varies proportionally to the amount of displacement. The electret mayalso be moved in the directions perpendicular to the opposing axis so asto vary the facing areas of the elements other than in the direction ofvarying in distance the gap between the electret and the inductionelectrode.

The embodiment shown in FIG. 2 utilizes the operation principle and hasthe purpose of application as the device in FIG. 1. However, amanipulatable or displaceable body such as field shielding plate 6 isinserted in the gap 4 between the electret l and the induction electrode3. If the dielectric flux in the gap 4 is varied by means of movement ofthe field shielding plate 6 which is grounded through "7, the electricresistance between the source S and drain D of the FET 5 variessubstantially linearly with respect to displacement of the fieldshielding plate, in accordance with the principle similar to that ofFIG. 1.

EXAMPLE 2 FIG. 3 is an explanatory view of operation of a contactlessswitch which is actuated by means of the elec tric potential of theelectret. In this example, there is employed an MOS-FET which has a gateleakage current far smaller than that of the general FET in order tostabilize the gate potential. Thus, due to the threshold voltage of theMOS-FET the OFF state becomes certain.

In FIG. 3, if the FET 5 is, for example, a P-channel enhancement typeMOS-FET having a threshold voltage, a minus face of the electret l isselected as the face which opposes the induction electrode 3. The otherface of the electret 1 is backed up with the rear electrode 2. The rearelectrode is connected to the source S of the F ET 5, the inductionelectrode 3 is connected to a first gate G, of the FET through avariable capacity diode 8. Between gate G and source S is coupled acapacitor 9 for adjusting the operation characteristics.

In the foregoing construction, if the electret l is sufficiently spacedapart from the induction electrode 3, the potential of the gate G, islower than the threshold voltage of the FET (in absolute value). Thus,the FET 5 is in the cut-off state between its source S and drain D.

If the electret 1 with the rear electrode 2 comes near to the inductionelectrode 3, the gate G is biased mainly by the variation of theelectrostatic capacitance between the induction electrode 3 andelectret 1. Therefore, the conductivity between the source S and drain Drises abruptly at a point exceeding the threshold value. The variablecapacity diode 8 compensates for potential lowering of the gate G due toits leakage current and, thus, is used to increase stability in thestatic ON state.

In connection with the above, variation of the electric field of theelectret relative to the induction electrode can also be caused byvarying the relative angle of the electret surface against the inductionelectrode or by the use of the field shielding plate as shown in FIG. 2.Further, it may be considered to cause the electric field of theelectret to act directly on the FETs channel without using the inductionelectrode to thereby modulate the electric conductivity of that FET.

FIG. 4 shows an element having a switch mechanism embodying theafore-said operation principle. In this drawing there are shown anelectret 1, the minus surface of which faces an induction electrode 3, aguide shaft 10 for backing up and supporting the electret 1 and operableto displace the electret 1 with respect to the induction electrode 3, apush button 11 secured on the top of the shaft 10, and a spring 12 forurging upward the electret 1 through the guide shaft 10, the foregoingmembers being held by an electrostatically shielded insulating outercasing 13. The FET 5, diode 8 and capacitor 9 are housed in a portion14, and the induction electrode 3, connection terminals 15 and 16 arewired in accordance with the circuit diagram shown in FIG. 3 or FIG. 4.Terminals l5 and 16 are connected, respectively, to the source S anddrain D. In such a switch element as shown above, an external electriccircuit connected between terminals 15 and 16 can provide, in responseto manipulation of the push button 11 of the switch element, withoutintervention of electric contacts, ON-OFF switching action or abruptvariation in the conduction state.

EXAMPLE 3 FIGS. 5 and 6 are explanatory views of proximity switchesusing the electret.

First, in FIG. 5 there are shown an electret 1, a rear electrode 2 forthe electret, a surface protecting film 17 of the electret, and an outercasing 18 for electrostatically shielding the foregoing elements bymeans of an insulation 19. The outer casing 18 is formed with a win dowin front of the electret l and at this window there is provided a metalnet 20 of an appropriate mesh size for protecting the inside andadjusting the operation characteristics. To the rear electrode 2 aswitch circuit similar to that of Example 2 shown in FIG. 3 isconnected.

In such electrode structure and circuit configuration including theelectret in a manner as above, the electric field distribution insideand outside the electret 1 varies in response to approach of aconductive or semiconductive body having an area so large as that of thewindow and being grounded, or approach of a dielectric body A which canchange the electrostatic capacitance appearing from the electret l tothe window largely as a grounded body does, towards the electret frontwin dow, that variation of the distribution being sensed by the FET 5through the rear electrode 2.

In the foregoing construction, if the input characteristic of the FET 5is made such as is the case of Example 2, the output end betweenelectrodes 8 and D ofthe FET is switched stably between ON and OFF uponapproach of the body.

FIG. 6 is an explanatory drawing of the proximity switch using a phasedetection system in order to improve the operation reliability inaccordance with the principle as above. The proximity switch of FIG. 5malfunctions possibly if it is operated in the ambient where staticelectricity generates or in the vicinity of a high voltage power source;thus, the embodiment of FIG. 5 is limited in its application condition.

In order to avoid the above limits, the detector of FIG. 6 isconstructed so that the electret 1 is rotated by a synchronous motor 22and the electric field of the electret l is sensed by the rear electrode21 in terms of an oscillating field of a certain frequency.

In more detail, a face 21' of the electret l facing its rear electrode21 is covered at its charging surface with a radial conductive sector 25having a certain number of wing portions to leave regularly spacedexposed portions and grounded therethrough, as shown in FIG. 7A. In FIG.7A, portions 26 are the exposed areas of the electret l, and the rearelectrode 21 has a shape analogous to the shape of the sector 25, asshown in FIG. 7B.

When the electret 1 having the foregoing configuration is rotated, thevoltage induced thereby in the rear electrode 21 becomes an oscillatingvoltage. The frequency of the induced voltage is determined by therevolution speed and the number of the wing portions, the magnitude isvaried by approach of various bodies (A) towards the front of theelectret 1 like the case of FIG. 5, and its variation is sensed by therear electrode 21, through a tuned amplifier 23 and phase detector 24,and output in the form of a DC. signal voltage. In this case, similarly,if the characteristic of the amplifier 23 is properly made non-linear, atwo-positional output signal can be realized in response to the approachof a body.

By the use of such a detection system as above, it is possible toisolate the field of the electret from the other static electricity andhigh voltage, and to ensure reliable operation of the proximity switch.The detection system can also be realized by the use of a vibrationsystem, other than the provision of rotating the electret.

It will be noted that, in the proximity switch, the approaching body canbe replaced by the induction electrode, then, the field distributionvariation of the electret due to approach of the body seems to be sensedby the rear electrode 2 or 21.

Although the invention has been described with respect to the preferredembodiments thereof, it is understood by those skilled in the art thatvarious modifications can be made in construction and arrangement withinthe scope of the invention as defined in the appended claims.

What is claimed is:

1. A method for controlling an electric circuit including a field effecttransistor, an electret and an induction electrode, comprising the stepsof;

coupling said induction electrode in an operable relationship to saidfield effect transistor; positioning said electret in spaced relation tosaid induction electrode such that said electret and induction electrodeare electrostatically coupled, and

selectively moving an electric field shielding plate into and out of thespace between said electret and said induction electrodes to control theoperating state of said field effect transistor.

2. A method for controlling an electric circuit including a field effecttransistor, an electret and an induction electrode said inductionelectrode being comprised of a plurality of symmetrically arranged wingportions, a face of said electret coinciding with said inductionelectrode being covered with a conductive film of the same pattern assaid induction electrode, comprising the steps of coupling saidinduction electrode in operable relation with said field effecttransistor, positioning said electret in spaced relation to saidinduction electrode to electrostatically couple said electret to saidinduction electrode, continuously rotating said electret relative tosaid induction electrode to provide a continuously oscillating electricfield therebetween to activate said field effect transistor at thefrequency of rotation of said electret and modulating the intensity ofsaid electric field by the movement of said induction electrode relativeto said electret, whereby the operating state of said field effecttransistor is controlled.

3. The method of claim 2 further including the step of moving a body inthe vicinity of said electric field to affect intensity modulation ofsaid electric field.

4. The method of claim 2 wherein the intensity modulation of saidoscillating electric field further includes the step of selectivelymoving an electric field shielding plate into and out of the spacebetween said electret and said induction electrode.

5. A device for controlling the operating state of a field effecttransistor comprising;

an electret, an induction electrode spaced from said electret togenerate an electric field therebetween,

means for electrically connecting the gate and source electrodes of saidfield effect transistor to said induction electrode and said electret,and

an electric field shielding electrode movably interposed in said spacebetween said electret and said induction electrode, whereby saidelectric field is varied in accordance with movement of said electricfield shielding electrode.

6. A device as claimed in claim 5 wherein said means for electricallycoupling includes a variable capacity diode serially coupled betweensaid gate of said field effect transistor and said induction electrodeand a capacitor connected between said gate and source electrodes.

7. A device for controlling the operating state of a field effecttransistor comprising:

an electret, an induction electrode spaced from said electret togenerate an electric field therebetween,

a casing for electrostatically shielding said electret and saidinduction electrode, said casing being provided with a window,

means for electrically connecting the gate and source electrodes of saidfield effect transistor to said induction electrode and said electret,and

a body facing said electret through said window to effect intensitymodulation of said electric field.

8. A device of claim 7 wherein said induction electrode is comprised ofa plurality of symmetrical winged sections and wherein the side of saidelectret facing said induction electrode is covered with a conductivefilm of the same pattern as said induction electrode, said devicefurther including means for continuously rotating said electret relativeto said induction electrode to generate an oscillating electric fieldtherebetween.

9. The device of claim 8 wherein said means for rotating comprises asynchronous motor, said device further including a tuned amplifier and aphase detector coupled to said induction electrode and a dielectric bodyfacing the side of said electret opposite the side facing said inductionelectrode to affect intensity modulation of said electric field.

1. A method for controlling an electric circuit including a field effect transistor, an electret and an induction electrode, comprising the steps of; coupling said induction electrode in an operable relationship to said field effect transistor; positioning said electret in spaced relation to said induction electrode such that said electret and induction electrode are electrostatically coupled, and selectively moving an electric field shielding plate into and out of the space between said electret and said induction electrodes to control the operating state of said field effect transistor.
 2. A method for controlling an electric circuit including a field effect transistor, an electret and an induction electrode said induction electrode being comprised of a plurality of symmetrically arranged wing portions, a face of said electret coinciding with said induction electrode being covered with a conductive film of the same pattern as said induction electrode, comprising the steps of coupling said induction electrode in operable relation with said field effect transistor, positioning said electret in spaced relation to said induction electrode to electrostatically couple said electret to said induction electrode, continuously rotating said electret relative to said induction electrode to provide a continuously oscillating electric field therebetween to activate said field effect transistor at the frequency of rotation of said electret and modulating the intensity of said electric field by the movement of said induction electrode relative to said electret, whereby the operating state of said field effect transistor is controlled.
 3. The method of claim 2 further including the step of moving a body in the vicinity of said electric field to affect intensity modulation of said electric field.
 4. The method of claim 2 wherein the intensity modulation of said oscillating electric field further includes the step of selectively moving an electric field shielding plate into and out of the space between said electret and said induction electrode.
 5. A device for controlling the operating state of a field effect transistor comprising; an electret, an induction electrode spaced from said electret to generate an electric field therebetween, means for electrically connecting the gate and source electrodes of said field effect transistor to said induction electrode and said electret, and an electric field shielding electrode movably interposed in said space between said electret and said induction electrode, whereby said electric field is varied in accordance with movement of said electric field shielding electrode.
 6. A device as claimed in claim 5 wherein said means for electrically coupling includes a variable capacity diode serially coupled between said gate of said field effect transistor and said induction electrode and a capacitor connected between said gate and source electrodes.
 7. A device for controlling the operating state of a field effect transistor comprising: an electret, an induction electrode spaced from said electret to generate an electric field therebetween, a casing for electrostatically shielding said electret and said induction electrode, said casing being provided with a window, means for electrically connecting the gate and source electrodes of said field effect transistor to said induction electrode and said electret, and a body facing said electret through said window to effect intensity modulation of said electric field.
 8. A device of claim 7 wherein said induction electrode is comprised of a plurality of sYmmetrical winged sections and wherein the side of said electret facing said induction electrode is covered with a conductive film of the same pattern as said induction electrode, said device further including means for continuously rotating said electret relative to said induction electrode to generate an oscillating electric field therebetween.
 9. The device of claim 8 wherein said means for rotating comprises a synchronous motor, said device further including a tuned amplifier and a phase detector coupled to said induction electrode and a dielectric body facing the side of said electret opposite the side facing said induction electrode to affect intensity modulation of said electric field. 